1. Field of the Invention
The present invention relates to a method of magnetic transfer and a magnetic recording medium, in particular to a method of magnetic transfer to write a servo signal or a special data on a magnetic recording medium using a magnetic transfer technology, the servo signal performing positioning of a magnetic head that reads and writes data recorded on the magnetic recording medium in a hard disk drive (an HDD). The present invention also relates to a magnetic recording medium including transfer information written by the method of magnetic transfer.
2. Description of the Related Art
Nowadays, magnetic information is written into a magnetic recording medium in the following way. A magnetic recording medium without any magnetic information written therein is installed in an HDD device. Then, necessary information is written in the HDD on concentric regions called tracks having a certain width on the magnetic recording medium.
Read/write of data is conducted while a magnetic head is moving along the track. The magnetic head is controlled not to deviate from the track by detecting positional difference between the magnetic head and the track according to a magnetic signal called a servo signal recorded on the magnetic recording medium.
In order to write a servo signal precisely in a configuration of a concentric circle on a magnetic recording medium that has no recorded data, a device having precise position control function needs to be inserted in every HDD from the outside, and it takes several hours for writing several hundred thousands of tracks on one surface of a magnetic recording medium. Enhancement of recording density at present days demands higher precision in the position control device and longer time for writing operation. Thus, the circumstances have been great demerits in productivity and costs with HDDs.
Accordingly, technologies and devices have been developed in which a master disk for magnetic transfer having a servo signal pattern is made to adhere to (put in close contact with) a magnetic recording medium, and an external magnetic field is applied to the adhered body (a combined structure of the master disk and the medium) and the servo signal pattern is transferred to the magnetic recording medium in a moment. This method can reduce the manufacturing cost of a drive and enhance track density (by decreasing the track width).
However, if an effort is made to adhere the master disk and the magnetic recording medium to each other, both having smooth surfaces, by bringing them into close contact over whole surfaces thereof at once, the process adherence from the beginning to the end proceeds essentially at random sequence within the surfaces. Consequently, air may be confined between the transferring surface and the transferred surface depending on the sequence of contact, thus creating an “air bubble”, which is a problem inhibiting sufficient contact between the transferring master disk and the transferred magnetic recording medium. Prescribed servo signal is not transferred in the air bubble, and a defect of “missing signal” is detected in the inspection on the magnetic recording medium after the transfer process.
To cope with this situation, Japanese Unexamined Patent Application Publication No. 2004-234710 discloses a method for uniform close contact with high precision between a transferring master disk and a transferred magnetic recording medium, in which the master disk and the medium are put in contact tightly in a pressurizing chamber or an evacuating chamber.
Japanese Unexamined Patent Application Publication No. H11-025455 discloses a method in which the transferring master disk is provided with grooves and holes for exhausting air, thereby making the master disk and the medium in tight contact by suction through the exhausting passage.
Japanese Unexamined Patent Application Publication No. 2003-173657 discloses a method of cleaning a master carrier in a process of transferring and recording a magnetic pattern corresponding to transfer information to a slave medium by making a master carrier carrying the transfer information and a slave medium receiving the transfer information in close contact and applying a magnetic field for magnetic transfer. In the method, the slave medium is subjected to verification inspection of the transferred magnetic pattern using a verification device. Based on the verification inspection, a part of the surface of the master carrier corresponding to the position of occurrence of the error is selectively cleaned to eliminate the deposited contaminant.
Japanese Unexamined Patent Application Publication No. 2006-127684 discloses an inspection method for detecting contamination on a master disk. In the method, a pair of master disks is pressed onto both surfaces of a magnetic disk to be transferred, and a magnetic field is applied to the pressed combination of the magnetic medium and the master disks to transfer the magnetic pattern on the surfaces of the master disks onto the both surfaces of the magnetic medium. After that, a light emission means emits light in such a way that the optical axis of the emission light takes an angle of 1 to 30 degrees with respect to a radial direction of an inspected part on the surface of the master disks and an imaging element of an imaging device takes images of the reflected light of the emitted light to inspect contamination.
However, in every prior art technologies with a master disk for magnetic transfer having a protruding contaminant adhered thereon, the contaminant inhibits tight contact and creates “an air bubble” around the contaminant. Unless eliminating the contaminant, the “missing signal” defects continue to be generated in the transferred media that are successively manufactured.
Occurrence of a defective contact due to the “air bubble” can only be detected by existence of the “missing signal” in the actually transferred medium. Consequently, great losses occur due to the time for inspecting every medium and defective media due to insufficient contact that are continuously produced during the inspecting period of time.
Although Japanese Unexamined Patent Application Publication No. 2006-127684 discloses an optical inspection method for a contaminant on the surface of a master disk after transferring the magnetic pattern thereon to a magnetic disk medium, the objects to be inspected are foreign matter of dusts and fibers adhered on the surface of the master disk and not an error of “missing signal” due to insufficient contact generated by an “air bubble”.